4 Acknowledgements And I would like to thank Andre-Luc Beylot and Anne Wei, my supervisors, for offering me the opportunity to pursue my doctoral studies at the Institute de Recherche en Informatique de Toulouse (IRIT), for their patience and insightful guidance. My special thanks to Tara Ali-Tahiya for her help, experience, guidance and advice in the resource allocation field. Thanks to the judge members for their hard work and the dedicated time when analysing my thesis. My special thanks to all my friends, secretaries and office mates for their support at the IRIT laboratory. Thanks to the Ecuadorian government for financing this thesis bythesecretaria Nacional de Educacion Superior, Ciencia y Tecnologia (SENESCYT). And finally my deepest gratitude to my parents, for their love, trustand support.

8 Abstract Driven by the growing demand for high-speed broadband wireless services, Long term Evolution (LTE) technology has emerged as a competitive alternative to mobile communications solution. In several countries around the world, the implementation of LTE has started. LTE offers an IP-based framework that provides high data rates for multimedia applications. Moreover, based on the 3GPP specifications, the technology providesa set of built in mechanisms to support heterogeneous classes of traffic including data, voice and video, etc. Supporting heterogeneous classes of services means that the traffic is highly diverse and has distinct QoS parameters, channel and environmental conditions may vary dramatically on a short time scale. The 3GPP specifications leave unstandardized the resource management and scheduling mechanisms which are crucial components to guarantee the QoS performance for the services. In this thesis, we evaluate the performance and QoS in LTE technology. Moreover, our research addresses the resource management and scheduling issues on the wireless interface. In fact, after surveying, classifying and comparing different scheduling mechanisms, we propose three QoS mechanisms for resource allocation in macrocell scenarios focused on real time services and two mechanisms for interference mitigation in femtocell scenariostaking into account the QoS of real time services. Our first proposed mechanism for resource allocation in macrocell scenarios combines the well known virtual token (or token buckets) method with opportunistic schedulers, our second scheme utilizes game theory, specifically the Shapley value in order to achieve a higher fairness level among classes of services and our third mechanism combines the first and the second proposed schemes. Our first mechanism for interference mitigation in femtocell scenarios is power control based and works by using non cooperative games. It performs a constant bargain between throughput and SINR to find out the

9 optimal transmit power level. The second mechanism is centralised, it uses abandwidthdivisionapproachinordertonotusethesamesubbands to avoid interference. The bandwidth division and assignation isperformed based on game theory (Shapley value) taking into account the application bitrate. This scheme reduces interference considerably and showsanimprovement compared to other bandwidth division schemes. All proposed mechanism are performed in a LTE simulation environment. several constraints such as throughput, Packet Loss Ratio, delay, fairness index, SINR are used to evaluate the efficiency of our schemes.

22 Introduction Motivation In recent years, operators across the world have seen a rapid growth of mobile broadband subscribers. At the same time, the traffic volume per subscriber is also increasing rapidly; in particular, with the introduction of more advanced mobile devices and real time services such as multimedia telephony and mobile TV. The introductionofthese new and demanding services such as audio, video streaming, interactive gaming with rapid response patterns has drawn attention toward possible limitationofthecapacity and Quality of Service (QoS). Since these services have different performance requirements, for example in terms of bit-rates and packet delays, under the partnership of the 3GPP, LTE (Long Term Evolution) is being introduced to fulfill this ambitious task. LTE is been deployed in Europe, USA and around the world. Thus, nowadays operators have already started to propose LTE technology to subscribers in order to provide high speed data rates. LTE offers a set of key features: (1) The use of Orthogonal Frequency Division Multiplex (OFDM), (2) time and frequency duplex (TDD and FDD), (3) support of Adaptive Modulation and Coding (AMC), (4) advanced antenna techniques such as Multiple Input Multiple Output (MIMO) and (5) QoS support. In thisthesis, weare mainly interested in the feature number five, QoS support. LTE architecturehasbeen developed to serve different classes of services such as video, VoIP,streaming,HTTP etc. However, the 3GPP specifications leave unstandardized the resource management and scheduling mechanism which are crucial components to guarantee QoS. One essential part for the QoS performance in LTE is the air interface. It is at the air interface where the physical resource allocation is performed. It is extremely important to provide an efficient resource allocation in order toguaranteeqosfor downlink and uplink systems. A non-efficient resource allocation might degrade the QoS among several services. Several services such as real time flows, require to be 1

23 INTRODUCTION treated taking into account several factors such as packet delays, bitrate, etc. The question to be asked here is How to distribute physical resources to an heterogeneous group of services that have heterogeneous requirements? Since this field has not been completely solved nowadays, the principal motivation for this thesis focuses on this approach. Specifically, we attack the physical resource allocation at the air interface because it is where an important part of the QoS is managed. In this thesis we evaluate the performance of LTE downlink system in mobile environments. Specifically, we investigate the potential and limitations that LTE possesses to perform real time services and consequently we propose several schemes to improve the QoS. This work mainly addresses the MAC layer considering thatresourcealloca- tion is carried out at this level. PHY layer is closely linked to this task, so in this thesis PHY layer is not neglected. This thesis is divided into two main parts. The first part is related to the resource allocation in downlink system in macrocell scenarios focused on real time services. In this part we present several solutions in order to improve the QoSlevel. Since operators have started to propose to subscribers femtocells (small base stations to be installed by users at home), the second part of our contributions aims to mitigate interference in femtocell scenarios to reach an enhancementofqosforrealtimeservices. Two schemes are made in contribution to this part of the thesis. The remainder of the thesis is organized as described in next section. Contributions and Outline Chapter 1: Overview of LTE The objective of this chapter is to provide a brief overview of LongTermEvolution technology. Firstly we go through the LTE architecture (EPC and e-utran), we describe the main entities of this architecture as its main functions. Several layers are in charge of the resource distribution performance, the physical layer (PHY), the Medium Access Control (MAC) layer and the Radio Link Control (RLC) layer. Unlike physical layer which is in charge of bit transmission, the Medium Access Control (MAC) layer is responsible for the wisely control of the strong characteristics that physical layer grants such as the optimal resource distribution among users. It is important to remark that resource allocation mechanisms can be performed by using cross-layer methods by interchanging parameters between MAC, PHY and RLC layers [2] [9]. This thesis does not present any cross-layer scheme, therefore in this chapter the layers overview is only 2

24 INTRODUCTION limited to the PHY and the MAC layers. Chapter 2: Overview of Resource Allocation Techniques In this chapter, we presentthe state of the art of resource allocation mechanisms for LTE downlink system. An in-depth analysis of existing methods and their characteristics is carried out. Proposed methods have been classified into groups based on their common characteristics. We also analyze the pros and cons of each family of schemes. All this information is taken into account when developing and presenting our schemes in chapter 3. Chapter 3: Downlink Radio Resource Allocation Strategies In order to improve the QoS in downlink system, in this chapter weproposethree schemes which focus on real time services. The first one adapts avirtualtokenmechanism to an opportunistic scheduler in order to improve the performance of real time services. In our second contribution, we combine game theory concepts(cooperative games) with opportunistic schemes in order to mitigate the lack of fairness among flows. In our third contribution, we combine our first two mechanisms toachieveanefficient trade-off between fairness and efficiency. We also evaluate the performance of several well known schedulers utilized in 3G technologies in order to compare them to our proposed solutions. Parts of this chapter were published in [86] [87] [38] and[90]. Chapter 4: An Overview of Femtocells In this chapter, we present a quick overview of femtocell architecture. We present a state of the art of femtocells focused on interference mitigation approaches. Several existing proposals are deeply analysed in order to expose the maincharacteristicsof each family of methods. Chapter 5: Interference Mitigation in Femtocells In this chapter, we focus on the improvement of QoS in downlink systeminfemtocell scenarios. We attack the neighboring interference problem by introducing two schemes. Our first contribution proposes to perform a fair sub-band division among femtocell neighbors based on game theory. This scheme is an improvement ofthewellknownfour colouring method for interference mitigation. Results show importantenhancementsof 3

25 INTRODUCTION performance. Thesecond proposedscheme performsan interference mitigation based on transmit power control. This scheme is also based on game theory in order to perform a constant bargain between the throughput game and the interference. Numerical results present considerable QoS improvements. This work has partly been accepted to be published in: [88] and[89] 4

26 Chapter 1 An overview of LTE As LTE technology becomes more widespread, concerns for the Quality of Service (QoS) in the wireless access network and backaul is at the forefront. In this thesis, we focus on the QoS for the wireless access network. However, it is important to provide a brief overview of the general LTE architecture standardized by the3gppspecifications. Firstly, we describe the general architecture of LTE. Concepts such as EPS, e- UTRAN are discussed. Secondly, we extend a general overview of the QoS architecture in LTE. In this part, we emphasize on how the QoS is handled. Finally, we present an overview of the LTE air interface. We detail the RLC, MAC and PHY layers which are closely related to the resource allocation performance. 1.1 LTE Architecture The result of the 3GPP standardization effort is the Evolved Packet System (EPS) that consists of the core network part, the Evolved Packet Core (EPC) and the radio network evolution part, the Evolved UTRAN (E-UTRAN), also known as LTE. The EPC can also be connected to other 3GPP and non-3gpp radio-access networks. As illustrated in Figure 1.1, theepcconsistsofsomecontrol-planenodes,calledmobility Management Entity (MME), control Home Subscriber Server (HSS) and two user-plane nodes, called Serving Gateway (S-GW) and Packet-data Network Gateway (P-GW). The LTE radioaccess network consists of the base stations, denoted as enhanced NodeB (enb), that are connected to each other through the X2 interface and to the EPCthroughtheS1 interface. The mobile terminal is denoted as User Equipment (UE). 5

27 1. An overview of LTE Figure 1.1: Overview of the EPC/LTE architecture Serving Gateway (S-GW): The S-GW maintains Service Data Flow (SDF) context for the default/dedicated bearers (explained in subsection 1.2.1) established.itisalso in charge of the mobility anchor for inter-enb and inter-3gpp accessmobilitypacket. Packet-data Network Gateway (P-GW): Is the entrance and the exit point for data traffic in the EPC. The P-GW performs policy enforcement and packet filtering for each data flow of each subscriber. It maintains the context foreachconnectionof the mobile device, the traffic flow templates for the active services, the QoS profile and the charging characteristics. Mobility Management Entity (MME): MME is the central management entity for the LTE accesses. It is responsible for the connection of the UE by selecting the gateway through which messages are to be exchanged and a level ofresourcesfortheue in cases of attachment and handover. It also provides authentication and authorization and location tracking using the HSS and intra-3gpp mobility (e.g. between 2G/3G 6

28 1. An overview of LTE and LTE). Home Subscriber Server (HSS): subscription data. The basic HSS function is the control of user Enhanced Node B (enb): The Enhanced Node B (enb) hosts the following functions; Radio Resource Management (Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink), IP header compression and encryption of user data stream, selection of an MME at UE attachment, routing of user plane data towards SAE Gateway,measurement and measurement reporting configuration for mobility and scheduling. The enb is in charge of an important QoS task which is the efficient performance of radio resource allocation. 1.2 Quality of Service (QoS) The QoS in LTE is composed of two main parts, the backhaul part which QoS architecture guarantees the efficient treatment of packet flows by the use of policies. This part focuses on QoS management between the gateways and the enb. It isatthegateway where the QoS parameters are set up in order to perform an efficient management of packet flows. The QoS management between the enb and UEs is performed by an entity called the Mac air interface. This entity located at the enb, is in charge of the final delivery of packet flows to UEs in a wireless environment The bearer The QoS concept in LTE brings out a central element called bearer. A bearer identifies packet flows that receive a common QoS treatment between theterminaland the gateway, see Figure 1.2. Allpacketflowsmappedtothesamebearerreceivethe same packet-forwarding treatment (e.g., scheduling policy, queue management policy, rate-shaping policy, link-layer configuration, etc.). There exist two types of bearers: Guaranteed Bit-Rate (GBR) and non-guaranteed Bit-Rate (non-gbr) [46]. Non-GBR bearers are also known as default bearers, and GBR-bearers are also known as dedicated bearers (Figure 1.3). Bearers are established, deleted and modified at the gateway by an entity called Policy Controller. The Policy Controller makesitsdecisionsbased on QoS parameters such as QoS Class Identifier (QCI), Allocation Retention Priority (ARP), Maximum Bit Rate (MBR), Guaranteed Bit Rate (GBR) [26]. 7

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